Date of Award

6-2026

Degree Name

MS in Polymers and Coatings

Department/Program

Chemistry & Biochemistry

College

College of Science and Mathematics

Advisor

Shanju Zhang

Advisor Department

Chemistry & Biochemistry

Advisor College

College of Agriculture, Food, and Environmental Sciences

Abstract

The increasing frequency and intensity of Wildland-Urban Interface (WUI) wildfires, such as the destructive 2025 Pacific Palisades Fire that destroyed over 6,000 structures, have underscored the urgent need for rapid post-fire safety assessment methodologies. This study sought to quantitatively characterize the Thermally Driven Red Hue Effect (TRHE), a unique, irreversible color shift observed in architectural coatings and concrete substrates, to determine its reliability as a permanent visual record of thermal exposure. Concrete substrates were formulated with three distinct coarse aggregates: gold granite (14.7% Fe), red cinder (22.4% Fe), and green rock (33.6% Fe) and coated with a 20 PVC waterborne latex coating that was either untinted (TiO₂ control) or tinted with yellow iron oxide (goethite). To simulate real-world coastal conditions, specimens were subject to accelerated saline spray exposure in a 5% NaCl QFOG chamber for up to 1,500 hours before being subjected to a twostep heat treatment reaching 400 °C or 500 °C. Quantitative results revealed that heat treatment was the primary driver of the TRHE, while saline spray exposure had a negligible effect on the magnitude of the color shift. The most dramatic response occurred in the yellow-coated systems, where the CIELAB a* coordinate increased from approximately 7.0 to 20–22, resulting in total color differences (∆𝐸 ∗ 𝑎𝑏) ranging from 24 to 27. X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) confirmed this shift was caused by the dehydroxylation and crystallographic transformation of yellow goethite pigment (α-FeOOH) into red hematite (α-Fe₂O₃). Thermogravimetric Analysis (TGA) showed that the organic binder matrix completely degraded between 400 °C and 460 °C, leaving behind an inorganic pigment residue. Uncoated concrete batches also exhibited a red shift, with a* values increasing by an additional 2–5 units as temperatures rose to 500 °C, primarily due to the oxidation of iron-bearing minerals in the aggregate. Furthermore, a telegraphing study with an as-applied contrast ratio of 0.96 ± 0.01 indicated that the reddening of the underlying substrate could influence the appearance of white coatings through incomplete hiding. These findings demonstrate that the TRHE is a predictable optical response that closely mirrors field observations from the Pacific Palisades Fire, suggesting that colorimetric analysis can serve as a valuable qualitative indicator for CAL FIRE to reconstruct fire behavior and streamline damage assessments in WUI communities.

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